Field of the Disclosure
The embodiments described herein relate to a method and system to increase the roughness of the gripping surface of coiled tubing injector head gripper blocks.
Description of the Related Art
Coiled tubing is used in various wellbore operations. FIG. 1 shows a trailer mounted coiled tubing reel 20 that stores the coiled tubing 30 prior to insertion into the wellhead 80. The coiled tubing 30 is unreeled and nominally straightened prior to insertion into the wellhead 80. An operator in a control cabin 10 controls the insertion of the coiled tubing 30. The coiled tubing 30 travels along a gooseneck 40 and into an injector head 100. A crane 50 is used to suspend the injector head 100 above the wellhead 80. Gripping blocks within the injector head 100 grip the coiled tubing 30 and are used to insert the coiled tubing 30 into the wellhead 80 as well as to remove the coiled tubing 30 from the wellhead 80. A stuffing box 60 positioned below the injector head 100 provides the primary operation seal between pressurized wellbore fluid and the surface. The coiled tubing 30 then travels through a blowout preventer (BOP) 70 and into the wellhead 80.
The gripper blocks within the injector head 100 support that coiled tubing 30 and are used to raise or lower the coiled tubing 30. The gripper blocks are pressed against the coiled tubing 30 to hold the coiled tubing 30 in place. The coiled tubing 30 is held in place by the friction force between the gripper blocks and the coiled tubing 30. The friction force is comprises of the normal force applied by the gripper blocks against the coiled tubing 30 and the coefficient of friction between the gripper blocks and the coiled tubing 30. As the weight of the coiled tubing 30 increases, the friction force may also need to increase to adequately support the coiled tubing 30. The friction force may be increased by either increasing the nominal force and/or increasing the coefficient of friction. The structural properties of the coiled tubing 30 may limit the total normal force that may be applied against the coiled tubing 30 without damaging the coiled tubing 30.
As the lengths of wellbores continue to increase, the weight of the coiled tubing string also increases. If the gripper blocks don't adequately support the coiled tubing 30, the coiled tubing 30 may slip within the injector head 100. Slippage of the coiled tubing 30 may cause at least two problems. Slippage may cause the coiled tubing 30 to become damaged. For example, slippage within the injector head 100 may cause the coiled tubing 30 to be gouged, potentially compromising the integrity of the coiled tubing, which may result in the expense of replacing the coiled tubing string. Secondly, most well intervention operations require precise positioning of a tool or bottom hole assembly connected to the coiled tubing 30. Slippage of the coiled tubing 30 through the coiled tubing 30 may interfere with precise positioning during well intervention operations. Thus, there is a need to prevent slippage of coiled tubing 30 within an injector head 100.